The present invention relates generally to constant xe2x80x9cRxe2x80x9d networks and, more particularly to a tapered constant xe2x80x9cRxe2x80x9d network for use in high power, high frequency distributed amplifiers.
High powered, high frequency distributed amplifiers are well known in the art, having been around since the 1940""s. Distributed or traveling wave techniques have been used to design distributed amplifiers comprising microwave GaAs FETs that operate from 2.0 to 20 GHZ. A discussion of distributed amplifier design is taught in the book entitled xe2x80x9cMicrowave Circuit Design Using Linear and Non-Linear Techniquesxe2x80x9d published by John Wiley and Sons in 1990, pages 350-369.
The aforementioned prior art reference teaches the use of both constant K and constant R networks comprising series inductances and shunt capacitances, the latter of which is generally provided by the parasitic drain-to-source capacitance of a FET that is coupled between the series inductances of the network. Multiple sections of these networks are generally cascaded together and, by adjusting the individual phase shift therethrough, the respective gains of each FET stage will add along the associated transmission lines, as is well understood.
Prior art constant xe2x80x9cRxe2x80x9d distributed amplifiers as aforementioned have generally been fabricated on GaAs substrates. Because the GaAs substrate is formed of a single layer, the efficiency and bandwidth of these amplifiers has been limited. One reason for this is that mutual conductance coupling factor of the series inductances is limited since the series inductance is formed, for an example, by using interwoven spiral transmission lines formed on the surface of the single layer substrate.
Hence, a need exists for an improved, high efficiency, broadband power amplifier.